Adhesive dispenser systems are used in several applications, including the deposition of structural adhesives onto parts, such as print cartridges. Current adhesive dispenser systems that use an auger to move the adhesive rely on adhesive material supply pressure cycling (on/off) and auger rotation to control the flow of adhesive material. However, compressibility of the adhesive in the supply system and the auger result in undesirable pressure transients in the supply system during pressure cycling. The auger and the supply system are open with respect to each other.
To control the dispensing, the supply system is often cycled between high and low pressure. The low pressure may be established to prevent the adhesive from leaking from the dispense tip, while the higher pressure is applied to direct the adhesive into the auger. The pressure cycling may result in the unintended leakage or drooling of material through the auger during dispensing processes. For example, during periods of low pressure some material can accumulate on the end of the dispense tip. When the pressure is then increased, the accumulated adhesive may result in an excess of material being deposited during the dispensing processes.
Other approaches are further used to minimize the amount of material that leaks or drools from the auger body when the auger is idle. For example, highly viscous material is used in combination with multiple flutes on the auger. These approaches only work with highly viscous materials in combination with auger assemblies having components with large coefficients of friction.
Still other systems have been developed that make use of needle valve, pinch valves, or other gate valves on the end of the auger assembly. Such methods add complexity, expense and/or the need for frequent cleaning or flushing of the valve parts. For example, when the auger assembly is replaced, the valves must be removed and cleaned. Once the auger assembly has been replaced, the valves are again coupled to the auger assembly. The cleaning and separate coupling operations increase maintenance costs.
Recently, systems have been developed that use displacement metering pumps to supply material to the auger. These displacement metering pumps may also be used as valves for the auger, in that they control the flow of the dispensed materials. These systems also add complexity and/or the need for frequent cleaning of the metering parts.